Furnace, kiln, or the like



A. BIGOT.

' FURNACE, KILN, OR THE LIKE. APPLICATION FILED NOV. 2. 1918.

1,404,427. Patented Jan. 24, 1922 2 SHEETS-SHEET l- A. BIGOT.

FURNACE; KILN, OR THE [.IKE- 7 APPLICATION FILED NOV. 2.1913- 1,404,427, Patented Jan. 24, 1922.

2 SHEETS-SHEET 2- UNITED STATES ALEXANDRE BIGOT, OF PARIS, FRANCE.

FURNACE, KILN, OR THE LIKE.

Application filed November 2, 1918.

To all whom it may concern:

Be it known that I, ALEXANDRE Brco'r, a citizen of France, residing in Paris, France, have invented certain new and useful Tmprot ements in or Relating to Furnaces, Kilns, or the like, of which the fOllOWiIlg is a specification.

The present invention has for its object an improved continuous furnace, capable of giving under applications requiring temperatures and dimensions comprised between the widest possible limits, a calorific capacity which is very high with a reduced amount of space occupied.

This furnace in its preferred embodiment belongs to the kind known as tunnel furnaces and is more particularly employed for rendering great services in the metal trades, the treatment of chemical products, glass making, manufacture of pottery, etc., where it ensures, both in the case of intermittent furnaces as Well as continuous or semi-continuous furnaces, a great economy in fuel, even in furnaces of small dimensions. The invention may be in part availed of in furnaces of other than tunnel type.

It is well known that the walls of furnaces, kilns, retorts and the like which are constructed of fire brick or ordinary brick, absorb a considerable amount of heat which is subsequently lost either in the ground or in the outer air. In certain apparatus such as the Hoifma-nn furnace which possesses thick walls, the amount of heat absorbed by the walls is greater than the amount necessary for heating the articles under treatment. In the case of continuous furnaces operated at high temperatures, such as tunnel furnaces, Siemens-Martin furnaces, or glass works furnaces, the loss of heat by radiation from the walls is so great that it becomes difficult for men to work in proximity to such furnaces when in operation.

This invention is designed to obviate these drawbacks, to reduce to a minimum the absorption of heat by the furnace walls, and to reduce the heat radiated into the air and conducted into the ground practically to the zero point; with the result that the heat which is prevented from escaping through the walls of the apparatus will act to produce a considerable rise of temperature within the furnace itself and will thus effect a great saving in fuel.

This invention is carried out by surround ing the apparatus, except at the openings of the same, by a thick layer of refractory Specification of Letters Patent.

Patented Jan. 24, 1922.

Serial No. 260,905.

substances of a heat-protecting and nonconducting character, these being made the subject of special choice and preparation. But inasmuch as these substances are lacking in mechanical strength, a special method of construction becomes necessary for such apparatus whereby the requisite strength and solidity shall be secured.

According to this invention, furnaces and like heating apparatus are composed essentially of three parts, as follows:

-First, an outer covering of an extremely rigid character which is closed at all parts, save at the openings of the apparatus and at the top, thus forming a sort of caisson enclosing within it the furnace or heating apparatus properly so-called.

Second, the furnace structure itself, which is disposed within the said rigid casing, and is usually constructed of refractory sub-i stances forming rather thin walls.

Third, the space between the apparatus and the said rigid casing is filled with suitable heat-protecting substances, such for instance as silica or Los Angeles kieselguhr, these being employed in the form of a very fine powder or of agglomerated masses of small apparent density.

The figures annexed to the present description, which are only given by way of example, relate to a method of practically carrying out the invention in the first case and to a modification in the second case. Fig. 1, is a cross section of the furnace. The left section showing the construction at the ends of the furnace and the right section the construction of the heating zone.

Fig. 2, is a cross section of a modification showing the use of baflies in con unction with the means for carrying the materials to be treated.

The furnace represented in transverse section in Figure 1 may serve for the treatment of materials which do not require a temperature of more than 1,400? C. In the left hand part, there has been illustrated a simple tunnel furnace heated by d rect flames passing over the goods; in the right hand half of this figure, is represented the same, with fiues made in the thickness of the walls, through which the flames pass, the goods being heated by radiation. This second arrangement allows the internal atmosphere of-the tunnel to be varled by admitting thereto other gases than air. The form, the position and the size of the fines are variable.

The receptacle which holds the goods is illustrated at a; it is constructed of special refractory materials and may, according to the materials to be treated, take the form of a simple plate, or even that of a box, or receptacle, etc. It rests upon balls at b, which roll along the ways 0 made in the slab of the bottom of the furnace which is itself of very refractory material.

The constitution of these different parts for the purpose of resisting high temperatures being impossible with the refractory materials ordinarily used (such as silica, silico-aluminous compounds, bauxite, and the like) I have been led to study compositions presenting the following qualities 1. Resistance, without deformation, to high temperatures with the charge of goods to be heated.

2. Conservation of an invariable volume after having been subjected to high temperatures.

3. Remaining compact and resistant after repeated beatings.

These results are obtained by the use for the composition of these parts of fused bauxites, corundums, and alumina, carborundum, compounds of chromium, magnesium, and rare earths such as the oxides of zirconium, cerium, and the like. These materials permit furthermore of giving to all these parts the reduced internal volume which it is proposed to carry out in the construction of the furnace.

The tunnel is constituted by the walls of of refractory bricks, which may either be solid, as is shown in the left hand part of the figure, or of special form to form the side passages as is shown in the right hand part.

In this latter case, particularly in those parts of the furnace which are subjected to a high temperature, the refractory elements are preferably constituted by refractory pieces 6, of high conductivity at a high temperature, (of carborundum, corundum, or the like, for example,) placed in the intenor; and of refractory pieces f, placed externally against the insulating material; the whole being fitted in to form the passages. The surfaces of the pieces 6 which are in contact with the flames may be augmented by the addition of teeth or ribs g or any other equivalent device.

In both forms of construction of the walls,

the whole rests upon a refractory block 71 of insulating bricks or of an insulating agglomerate. The tunnel is covered in with an lnsulating material it over the whole of the remaining portion of its surface.

In order to use the most highly insulating materials I have had recourse to the construction of. a heat retaining jacket, having a very rigid casing while being of small thlckness, and containing insulating materials in powder or in agglomerates in order to obtain the maximum insulation.

The results of experiments made have shown that the incombustible materials of highest insulating power are presented in the form of light powders, suchas the powder of light magnesia, light silicates, and the like.

The substances which are found most suitable for this use and which best possess the re uisite qualities, are the light silicates, eit ier in the natural state or obtained by precipitation, precipitated glucine, light magnesia, and the like, but in practice and by reason of their cheapness, I employ preferably the lightest of the infusorial silicates or diatom silicates (kieselguhr). Vhen in the form of a light and non-packed powder, these silicates will absorb from 30 to 40 times less heat than the ordinary brick or fire brick, and are partially substituted for the same in the construction. In the form of agglomerated material obtained by furnace treatment or by mixing'with lime, these silicates will absorb from 10 to 15 times less heat than ordinary brick or fire brick, for which they are partially substituted in this invention. Their heat-protecting power is due to the air which is contained in their pores. The lighter these substances are, the more air they will contain and the greater will be their non-conducting properties. The above-mentioned substances are selected among the lightest of this class. In order to impart the necessary rigidity to the tunnel, small cross walls are constructed between the casing and this tunnel. For the purpose of reducing to its lowest limit, the loss by permeability in these small walls, they are constructed of insulating agglomerates, and will be of slight thickness and also relatively spaced apart; they will be located opposite frames forming part of the general skeleton of the furnace; these frames will also be constituted by posts m, m cross beams n and bearers 0. A thin vertical filling of bricks, will, as much as the small walls, prevent deformation of the carcass and ensure the walls being gas tight.

In the modification shown in Figure 2, in order to abstract to the desired extent the balls and the ways from the influence of too high a. temperature which would bring about their deformation, the plates carrying the materials do not rest directly on the balls, but on the contrary through the medium of an insulating block p. The access of the heat to the lower part of the structure is largely diminished by the edges of the plate 9 and the corresponding edges 1 of the side walls of the tunnel. In this way, the temperature in the furnace so high in itself, does not run the risk of impairing the strength of the parts which carry the oods.

In the apparatus constructed according to this invention, the entire base, upon which is disposed the bottom of the furnace and the non-conducting side walls, is provided in its interior with non-conducting agglomerated material of suitable thickness. Upon such heat-insulating base are erected the refractory portions of the apparatus such as furnaces, gas producers and the like. The space which is left empty between the inner refractory wall and the outer rigid wall, may be filled in with the same light agglomerated material. In practice the thickness of the latter should not be much below one foot. The vault and the top of the apparatus may likewise be covered with such light agglomerated substances for the same or a greater thickness. The strength of this material against crushing strain should be such that it will not become crushed under the effect of the expansion of the walls of the apparatus when this latter is heated up.

Instead of employing this arrangement, it is found preferable in a great number of cases to replace the light agglomerated. substances by the said light powder, which has much better heat-protecting properties, in all the vertical portions, and upon the vault of the apparatus. The thickness of the layer of powder may be increased to two feet at the hottest parts of the apparatus. To prevent the interior refractory construction from getting out of shape by the action of heat. vertical brick partitions are constructed which are suitably spaced apart, these being connected at one end thereof with the fire brick of the apparatus, while at the other end, they enter into contact with the inner side of the rigid wall which constitutes the outer casing. This construction will form a series of chambers which are then filled in with a very light kieselguhr powder which is not packed down. The top of the apparatus is thereupon covered with this same powder. The thickness of the layer of powder will vary according to the heat to be employed in the apparatus. Should it be desired to attain 1400 C. or over, the thickness must be over one foot. By using a thickness of 50 centimeters, the heat conducted through the powdered substance to the outer casing will be very small.

The hereinbefore described construction is applicable to all varieties of furnaces, kilns, gas producers, and the like.

The furnace constructed according to this invention presents incontestable economical qualities over other furnaces of this type. Even at high temperatures it utilizes up to 7 /10ths of the calories emitted by the grates, the intermittent furnaces utilizing scarcely 1/ 10th of the calories and the tunnel furnaces now known not utilizing more than 5/l0ths of the calories. It also permits of the attainment of much higher temperatures than with the existing models and occasions, in comparison with furnaces with metal trucks, a great simplicity of mechanism, avoiding at the same time a notable loss of heat.

It is shown by experience that the temperature of the air in the neighborhood of such apparatus is scarcely higher than in the outer air. In the case of a gas producer thus constructed, and operating upon coke fuel. the temperature of the combustible gases leaving the apparatus exceeds 1 000 c.

The construction is very light as it requires only a relatively limited quantity of refractory bricks and insulating bricks, the surplus for the filling being formed by raw materials, whence an appreciable economy results. Finally the calorific advantages obtained with this furnace are independent of the dimensions and proportions thereof; in particular it is possible to carry out, with this kind of construction, furnaces of very small dimensions of high calorific efficiency.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is 1. A furnace comprising an inner portion of refractory material, an outer enclosing casing, and an intervening heat-insulating body of light pulverulent material of low heat conductivity.

2. A furnace comprising an inner portion of refractory material, an outer enclosing casing. and an intervening heat-insulating body of agglomerated material of low heat conductivity interspersed with minute cavities.

3. A furnace according to claim 1, the heat insulating material being in the nature of magnesia, infusorial silica or the like, the particles of which afford minute surface contact and are interspersed by minute interstices enclosing air.

4. A furnace according to claim 2, the heat-insulating material being in the nature of magnesia, infusorial silica or the like, the particles of which afford minute surface contact.

5. A furnace according to claim 1, the outer casing being formed of masonry.

6. A furnace according to claim 1, having an underlying heat-insulating base of light agglomerated material of low heat conductivity interspersed with minute cavities.

In witness whereof I have hereunto signed my name.

ALEXANDRE BIGOT. 

